fix: preserve user-specified order for BYHOUR/BYMINUTE with BYSETPOS

rrule.go

@@ -249,7 +249,6 @@ func buildRRule(arg ROption) RRule {
 				}
 			}
 		}
-		sort.Sort(timeSlice(r.timeset))
 	}
 
 	r.Options = arg

rrule_test.go

@@ -4010,3 +4010,143 @@ func iterateNum(iter Next, num int) (last time.Time) {
 	}
 	return last
 }
+
+// TestBySetPosWithNonSortedByhourByminute tests that BYSETPOS correctly
+// references positions in the timeset when BYHOUR and BYMINUTE values
+// are specified in non-chronological order.
+// This is a regression test for the bug where the timeset was incorrectly
+// sorted, causing BYSETPOS to select wrong time combinations.
+//
+// Example: BYHOUR=3,6 BYMINUTE=45,15 should generate timeset:
+//   [03:45, 03:15, 06:45, 06:15]
+// BYSETPOS=1,4 should select positions 1 and 4:
+//   03:45 (position 1) and 06:15 (position 4)
+//
+// Before the fix, the timeset was sorted to [03:15, 03:45, 06:15, 06:45],
+// causing BYSETPOS=1,4 to incorrectly select 03:15 and 06:45.
+func TestBySetPosWithNonSortedByhourByminute(t *testing.T) {
+	r, err := NewRRule(ROption{
+		Freq:     DAILY,
+		Interval: 1,
+		Count:    8,
+		Dtstart:  time.Date(2025, 3, 21, 0, 0, 0, 0, time.UTC),
+		Byhour:   []int{3, 6},
+		Byminute: []int{45, 15},
+		Bysetpos: []int{1, 4},
+	})
+	if err != nil {
+		t.Fatalf("failed to create RRule: %v", err)
+	}
+
+	value := r.All()
+
+	// Expected: each day should have 03:45 and 06:15 (not 03:15 and 06:45)
+	// The timeset is built as [03:45, 03:15, 06:45, 06:15] based on BYHOUR/BYMINUTE order
+	// BYSETPOS=1,4 selects position 1 (03:45) and position 4 (06:15)
+	want := []time.Time{
+		time.Date(2025, 3, 21, 3, 45, 0, 0, time.UTC),
+		time.Date(2025, 3, 21, 6, 15, 0, 0, time.UTC),
+		time.Date(2025, 3, 22, 3, 45, 0, 0, time.UTC),
+		time.Date(2025, 3, 22, 6, 15, 0, 0, time.UTC),
+		time.Date(2025, 3, 23, 3, 45, 0, 0, time.UTC),
+		time.Date(2025, 3, 23, 6, 15, 0, 0, time.UTC),
+		time.Date(2025, 3, 24, 3, 45, 0, 0, time.UTC),
+		time.Date(2025, 3, 24, 6, 15, 0, 0, time.UTC),
+	}
+
+	if !timesEqual(value, want) {
+		t.Errorf("BYSETPOS with non-sorted BYHOUR/BYMINUTE failed.\ngot:  %v\nwant: %v", value, want)
+	}
+}
+
+// TestBySetPosPreservesTimesetOrder verifies that the timeset order
+// is preserved based on the order of BYHOUR and BYMINUTE values,
+// not sorted chronologically. This ensures BYSETPOS works correctly.
+//
+// The timeset is generated by iterating BYHOUR then BYMINUTE:
+//   for hour in BYHOUR:
+//     for minute in BYMINUTE:
+//       timeset.append(hour:minute)
+//
+// For example, BYHOUR=[6,3] BYMINUTE=[30,0] generates:
+//   [06:30, 06:00, 03:30, 03:00]
+// NOT the sorted order [03:00, 03:30, 06:00, 06:30]
+func TestBySetPosPreservesTimesetOrder(t *testing.T) {
+	tests := []struct {
+		name     string
+		byhour   []int
+		byminute []int
+		bysetpos []int
+		wantHM   [][2]int // expected hour:minute pairs
+	}{
+		{
+			// timeset: [06:30, 06:00, 03:30, 03:00]
+			// BYSETPOS=1,4 selects positions 1 and 4: 06:30 and 03:00
+			// Results are returned chronologically: 03:00, then 06:30
+			name:     "reverse order hours and minutes",
+			byhour:   []int{6, 3},
+			byminute: []int{30, 0},
+			bysetpos: []int{1, 4},
+			wantHM:   [][2]int{{3, 0}, {6, 30}},
+		},
+		{
+			// timeset: [12:15, 12:45, 08:15, 08:45]
+			// BYSETPOS=2,3 selects positions 2 and 3: 12:45 and 08:15
+			// Results are returned chronologically: 08:15, then 12:45
+			name:     "mixed order",
+			byhour:   []int{12, 8},
+			byminute: []int{15, 45},
+			bysetpos: []int{2, 3},
+			wantHM:   [][2]int{{8, 15}, {12, 45}},
+		},
+		{
+			// timeset: [09:45, 09:30, 09:15, 09:00]
+			// BYSETPOS=1,4 selects positions 1 and 4: 09:45 and 09:00
+			// Results are returned chronologically: 09:00, then 09:45
+			name:     "single hour multiple minutes",
+			byhour:   []int{9},
+			byminute: []int{45, 30, 15, 0},
+			bysetpos: []int{1, 4},
+			wantHM:   [][2]int{{9, 0}, {9, 45}},
+		},
+		{
+			// timeset: [03:45, 03:15, 06:45, 06:15]
+			// BYSETPOS=-4,-1 selects positions -4 (=1) and -1 (=4): 03:45 and 06:15
+			// Results are returned chronologically: 03:45, then 06:15
+			name:     "negative bysetpos",
+			byhour:   []int{3, 6},
+			byminute: []int{45, 15},
+			bysetpos: []int{-4, -1},
+			wantHM:   [][2]int{{3, 45}, {6, 15}},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			r, err := NewRRule(ROption{
+				Freq:     DAILY,
+				Count:    len(tt.wantHM),
+				Dtstart:  time.Date(2025, 1, 1, 0, 0, 0, 0, time.UTC),
+				Byhour:   tt.byhour,
+				Byminute: tt.byminute,
+				Bysetpos: tt.bysetpos,
+			})
+			if err != nil {
+				t.Fatalf("failed to create RRule: %v", err)
+			}
+
+			value := r.All()
+			if len(value) != len(tt.wantHM) {
+				t.Fatalf("got %d results, want %d", len(value), len(tt.wantHM))
+			}
+
+			for i, v := range value {
+				gotH, gotM := v.Hour(), v.Minute()
+				wantH, wantM := tt.wantHM[i][0], tt.wantHM[i][1]
+				if gotH != wantH || gotM != wantM {
+					t.Errorf("result[%d]: got %02d:%02d, want %02d:%02d", i, gotH, gotM, wantH, wantM)
+				}
+			}
+		})
+	}
+}